Self-light-emitting device and method of manufacturing the same

ABSTRACT

Failure light emission of an EL element due to failure film formation of an organic EL material in an electrode hole  46  is improved. By forming the organic EL material after embedding an insulator in an electrode hole  46  on a pixel electrode and forming a protective portion  41   b , failure film formation in the electrode hole  46  can be prevented. This can prevent concentration of electric current due to a short circuit between a cathode and an anode of the EL element, and can prevent failure light emission of an EL layer.

This application is a divisional of U.S. application Ser. No. 11/592,575filed on Nov. 3, 2006 now U.S. Pat. No. 7,732,824 which is continuationof U.S. application Ser. No. 10/929,896 filed on Aug. 30, 2004 (now U.S.Pat. No. 7,132,693 issued Nov. 7, 2006) which is a continuation of U.S.application Ser. No. 09/782,239, filed on Feb. 13, 2001 (now U.S. Pat.No. 6,833,560 issued Dec. 21, 2004).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a self-light-emitting device(also referred to as an EL device). In particular, the present inventionrelates to such a self-light emitting device in which an EL element,which is constructed of an anode, a cathode, and a light emittingorganic material (hereinafter, referred to as organic EL material) withwhich EL (electro luminescence) is obtained, is sandwiched therebetween,is formed on an insulator, and to a method of manufacturing electricequipment having the self-light-emitting device as a display portion(display or display monitor). Note that in this specification, adescription will be made of an EL display device as the above statedself-light-emitting device.

2. Description of the Related Art

In recent years, the development of display devices using an EL element(EL display device) as a self-light-emitting element which utilizes theEL phenomenon of light emitting organic material has been advancing. TheEL display device is a self-light-emitting device, and therefore itdoesn't need a back light such as that of a liquid crystal displaydevice. In addition, the EL display device has a wide angle of view. Asa result, the El display device is looked upon as promising as a displayportion of electric equipment.

EL display devices are classified into two: a passive type (simplematrix type); and an active type (active matrix type), both of whichhave been actively developed. Particularly, the active matrix EL displaydevice is attracting attention these days. With regard to organic ELmaterials to be an EL layer which can be said to be the center of an ELelement, low molecular weight organic EL materials and high molecular(polymer) organic EL materials have been studied. The low molecularweight organic EL materials are formed by vapor deposition or the like,while the high molecular organic EL materials are formed through acoating using a spinner.

With respect to both the low molecular weight organic EL material andthe high molecular (polymer) organic EL materials, when the surface onwhich the EL material is formed is not planarized, there is a problem inthat the thickness of the formed EL material can not be even.

Further, in case that the thickness of the EL layer is not even and theEL layer is partly not formed at a step portion, when an EL elementformed of a cathode, the EL layer, and an anode is formed, the cathodeand the anode are short-circuited.

When the cathode and the anode are short-circuited, electric currentintensively flows between the cathode and the anode, and almost noelectric current flows through the EL layer, which makes the EL layernot to emit light.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is to improve the structure of an EL element,and to provide a method of manufacturing an EL display device. Moreover,another object of the present invention is to provide an electricequipment having such an EL display device as a display portion.

In order to attain the above objects, according to the presentinvention, there is employed a structure such that when an EL layer isformed by an organic EL material for forming the EL layer, an insulatoris embedded to planarize an uneven portion on the surface where theorganic EL material is to be formed, thereby preventing a short circuitbetween a cathode and an anode in an EL element from occurring. FIGS. 1Ato 1C illustrate the structure of cross sections of a pixel portion ofan EL display device according to the present invention.

FIG. 1A illustrates a TFT for controlling electric current, which iselectrically connected to a pixel electrode 40. After a base film 12 isformed on a substrate 11, the TFT for controlling electric current isformed so as to have an active layer including a source region 31, adrain region 32, and a channel forming region 34, a gate insulating film18, a gate electrode 35, a first interlayer insulating film 20, a sourcewiring 36, and a drain wiring 37. Note that, although the gate electrode35 is of a single-gate structure in the figure, it may be of amulti-gate structure.

Then, a first passivation film 38 is formed at the thickness of 10 nm to1 μm (preferably 200 to 500 nm). As the material, an insulating filmcontaining silicon (especially, a silicon oxynitride film or a siliconnitride film is preferable) can be used.

A second interlayer insulating film (which may also be referred to asplanarizing film) 39 is formed on the first passivation film 38 so as tocover the respective TFTs to planarize a step formed by the TFTs. As thesecond interlayer insulating film 39, an organic resin film such as apolyimide resin, a polyamide resin, an acrylic resin, or a resincontaining a high molecular compound of siloxane is preferable. Ofcourse, an inorganic film may also be used if it can perform sufficientplanarization.

It is quite important to planarize, by the second interlayer insulatingfilm 39, a step formed by the TFTs. Since an EL layer to be formed lateris very thin, existence of a step may cause failure light emission.Therefore, it is preferable that planarization is performed prior to theformation of the pixel electrode in order to make as planar as possiblethe surface on which the EL layer is formed.

Further, reference numeral 40 denotes a pixel electrode (correspondingto an anode of the EL element) formed of a transparent conductive film,and is formed so as to be connected to the drain wiring 37 of the TFTfor controlling electric current through a contact hole (opening) whichis formed in the second interlayer insulating film 39 and the firstpassivation film 38.

According to the present invention, as the pixel electrode, a conductivefilm formed of a compound of indium oxide and tin oxide is used. A smallamount of gallium may be doped into the compound. Moreover, a compoundof indium oxide and zinc oxide, or a compound of zinc oxide and galliumoxide may be used.

Note that a concave portion 46, formed after the pixel electrode isformed in the contact hole, is herein referred to as an electrode hole.After the pixel electrode is formed, an EL material is formed to form anEL layer. In this case, however, as shown in FIG. 1B, the thickness ofthe EL layer in the electrode hole 46 becomes thinner in thin filmregion 47. Though the extent of the thinning of the film thicknessdepends on the tapered angle of the electrode hole, among the filmforming surfaces, portions which are not vertical with respect to thefilm forming direction tend to have difficulty in having the formed filmand tend to have thinner film thickness.

However, if the formed EL layer becomes thinner here, and in addition, adisconnected portion is formed, the cathode and the anode in the ELelement are short-circuited, and electric current intensively flowsthrough this short-circuited portion. This prevents electric currentfrom flowing through the EL layer, which makes the EL layer not to emitlight.

Accordingly, in order to prevent the short circuit between the cathodeand the anode in the EL element, an organic resin film is formed on thepixel electrode so as to sufficiently fill up the electrode hole 46. Bypatterning the formed organic resin film, a protective portion 41 b isformed. In other words, the protective portion 41 b is formed so as tofill up the electrode hole. Note that a similar protective portion (notshown) of an organic resin film may also be formed in a space betweenpixel electrodes so as to fill up the space.

The organic resin film is formed by spin coating. After exposing theorganic resin film to light using a resist mask, etching is performed toform the protective portion 41 b as illustrated in FIG. 1C.

Note that the thickness of a rising portion in cross section of theprotective portion 41 b from the pixel electrode (a portion illustratedas Da in FIG. 1C) is 0.1 to 1 μm, preferably 0.1 to 0.5 μm, morepreferably 0.1 to 0.3 μm.

Also, the material of the protective portion 41 b is preferably anorganic resin such as a polyimide resin, a polyamide resin, an acrylicresin, or a resin containing a high molecular compound of siloxane.Further, the viscosity of such an organic resin used is preferably 10⁻³Pa·s to 10⁻¹ Pa·s.

After the protective portion 41 b is formed, as illustrated in FIG. 1C,an EL layer 42 is formed, and further, a cathode 43 is formed. Note thatthe EL material forming the EL layer 42 may be a low molecular weightorganic EL material and may be a high molecular organic EL material.

By forming the structure illustrated in FIG. 1C as in the above, theproblem of the short circuit between the pixel electrode 40 and thecathode 43 caused when the EL layer 42 is disconnected at a step portionin the electrode hole 46 can be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views showing cross sections of a pixel portion;

FIG. 2 is a view showing a cross section of the pixel portion;

FIGS. 3A and 3B are views showing a top surface and a structure of thepixel portion, respectively;

FIGS. 4A to 4C are views showing cross sections of a pixel portion;

FIGS. 5A to 5C are views showing cross sections of a pixel portion;

FIGS. 6A to 6E are views showing a manufacturing process of an ELdisplay device;

FIGS. 7A to 7D are views showing a manufacturing process of the ELdisplay device;

FIGS. 8A to 8C are views showing a manufacturing process of the ELdisplay device;

FIG. 9 is a view showing an element structure of a sampling circuit;

FIG. 10 is a view showing an appearance of the EL display device;

FIG. 11 is a diagram showing a circuit block structure of the EL displaydevice;

FIGS. 12A and 12B are views showing cross sections of an active matrixtype EL display device;

FIGS. 13A to 13D are views showing cross sections of a pixel portion;

FIG. 14 is a view showing a cross section of a passive type EL displaydevice;

FIGS. 15A to 15F are views showing specific examples of electricequipment; and

FIGS. 16A and 16B are views showing specific examples of electricequipment

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

An embodiment mode of the present invention will be explained using FIG.2 and FIGS. 3A and 3B. Shown in FIG. 2 is a cross sectional view of apixel portion of an EL display according to the present invention. FIG.3A shows a top view of the pixel portion, and FIG. 3B is a circuitstructure of the pixel portion. In practice, a pixel portion (imagedisplay portion) is formed in which a plurality of pixels are arrangedin matrix. Note that the cross sectional diagram taken along the lineA-A′ of FIG. 3A corresponds to FIG. 2. Common reference symbols are usedin FIG. 2 and FIGS. 3A and 3B, and therefore both figures may besuitably referenced. Further, two pixels are shown in the top views ofFIG. 3A, however either has the same structure.

In FIG. 2, reference numeral 11 denotes a substrate, and referencenumeral 12 denotes an insulating film which becomes a base (hereafterreferred to as base film). A substrate made from glass, glass ceramic,quartz, silicon, ceramic, a metal, or a plastic may be used as thesubstrate 11.

Further, although the base film 12 is especially effective for cases inwhich a substrate containing mobile ions, or a substrate havingconductivity is used, it need not be formed for a quartz substrate. Aninsulating film containing silicon may be formed as the base film 12.Note that, in this specification, the term “insulating film containingsilicon” indicates, specifically, an insulating film such as a siliconoxide film, a silicon nitride film, or an silicon oxynitride film(denoted by SiOxNy) containing silicon, oxygen, and nitrogen inpredetermined ratios.

Further, the dispersion of TFT generated heat by giving the base film 12a heat radiating effect is effective in preventing TFT degradation or ELelement degradation. All known materials may be used in giving the heatradiating effect.

In this case, two TFTs are formed within the pixels. Reference numeral201 denotes a switching TFT formed by an n-channel TFT, and referencenumeral 202 denotes an electric current controlling TFT, formed by ap-channel TFT.

Note that it is not necessary to place limitations on the presentinvention such that the switching TFT is an n-channel TFT and theelectric current controlling TFT is a p-channel TFT, and that it ispossible to form the switching TFT using a p-channel TFT and to form theelectric current controlling TFT using an n-channel TFT. It is alsopossible to use n-channel TFTs for both, and to use p-channel TFTs forboth.

The switching TFT 201 is formed with: an active layer containing asource region 13, a drain region 14, LDD regions 15 a to 15 d, a highconcentration impurity region 16, and channel forming regions 17 a and17 b; a gate insulating film 18; gate electrodes 19 a and 19 b, a firstinterlayer insulating film 20, a source wiring 21, and a drain wiring22.

Further, as shown in FIGS. 3A and 3B, this is a double gate structure inwhich the gate electrodes 19 a and 19 b are electrically connected by agate wiring 211 formed by a different material (a material having alower resistance than the gate electrodes 19 a and 19 b). Of course, inaddition to the double gate structure, a single gate structure or amulti-gate structure (a structure containing an active layer having twoor more channel forming regions connected in series) may also beemployed. The multi-gate structure is extremely effective in loweringthe value of the off current. Therefore, a switching element having alow off current value is realized with the present invention by using amulti-gate structure for the switching element 201.

Further, the active layer is formed of a semiconductor film containing acrystal structure. Namely, the active layer may be formed using a singlecrystal semiconductor film, a polycrystal semiconductor film, or amicrocrystal semiconductor film. Further, the gate insulating film 18may be formed of an insulating film containing silicon. In addition, allconductive films may be used for the gate electrodes, the source wiring,and the drain wiring.

In addition, the LDD regions 15 a to 15 d in the switching TFT 201 areformed sandwiching the gate insulating film 18, and so as not to overlapthe gate electrodes 19 a and 19 b. Such structure is extremely effectivein reducing the off current value.

Note that the formation of an offset region (a region having thesemiconductor layer with the same composition as the channel formingregions, and to which a gate voltage is not applied) between the channelforming regions and the LDD regions is additionally preferable forreducing the off current value. Further, when a multi-gate structurehaving two or more gate electrodes is used, a high concentrationimpurity region formed between the channel forming regions is effectivein lowering the value of the off current.

Next, the current controlling TFT 202 is formed with having: an activelayer containing a source region 31, a drain region 32, and a channelforming region 34; the gate insulating film 18; a gate electrode 35; thefirst interlayer insulating film 20; a source wiring 36; and a drainwiring 37. Note that the gate electrode 35 has a single gate structure,however a multi-gate structure may also be used.

As shown in FIG. 2, the drain of the switching TFT 201 is electricallyconnected to the gate of the current controlling TFT 202. Specifically,the gate electrode 35 of the current controlling TFT 202 is electricallyconnected to the drain region 14 of the switching TFT 201 through thedrain wiring (also referred to as connection wiring) 22. Further, thesource wiring 36 is connected to an electric power supply line 212.

The current controlling TFT 1202 is an element for controlling theamount of current injected into an EL element 203. However, ifdeterioration of the EL element is considered, it is not preferable thattoo much current is allowed to flow. It is therefore preferable todesign the channel length (L) to be long so that an excess current doesnot flow in the current controlling TFT 202. The amount of current ispreferably from 0.5 to 2 μA (more preferably between 1 and 1.5 μA) perpixel.

Also, the length (width) of the LDD regions formed in the switching TFT201 may be set within a range of from 0.5 to 3.5 μm, typically between2.0 and 2.5 μm.

Further, as illustrated in FIG. 3, in a region denoted as 50, throughthe gate insulating film, the wiring 36 that becomes the gate electrode35 of the TFT 202 for controlling electric current overlaps asemiconductor film 51 which is formed simultaneously with the activelayer. At this time, in the region 50, a capacitor is formed andfunctions as a storage capacitor 50 for storing voltage applied to thegate electrode 35 of the TFT 202 for controlling electric current. Inaddition, a capacitor formed of the wiring 36 that becomes the gateelectrode, a first interlayer insulating film (not shown), and a powersupply line 212 also forms the storage capacitor 50. Note that a drainof the TFT for controlling electric current is connected to the powersupply line 212, and constant voltage is always applied to the drain.

Further, seen from the viewpoint of increasing the amount of currentwhich is allowed to flow, it is effective to make the film thickness ofthe active layer (especially the channel forming region) of the currentcontrolling TFT 202 thick (preferably from 50 to 100 nm, more preferablybetween 60 and 80 nm). Conversely, seen from the point of view of makingthe off current value smaller for the switching TFT 201, it is alsoeffective to make the film thickness of the active layer (especially thechannel forming region) thin (preferably from 20 to 50 nm, morepreferably between 25 and 40 nm).

Next, reference numeral 38 denotes a first passivation film, and itsfilm thickness may be set from 10 nm to 1 μm (preferably between 200 and500 nm). An insulating film containing silicon (in particular, it ispreferable to use an silicon oxynitride film or a silicon nitride film)can be used as the passivation film material.

A second interlayer insulating film (this may also be referred to as aplanarizing film) 39 is formed on the first passivation film 38 so as tocover each TFT, and performs the planarizing of steps of the TFTs. Anorganic resin film is preferable as the second interlayer insulatingfilm 39, and resin materials such as an acrylic resin, and resinscontaining a high molecular compound of polyimide, polyamide, andsiloxane may be used. An inorganic film may also be used, of course,provided that it is capable of sufficient planarizing.

It is extremely important to planarize the steps of TFTs by the secondinterlayer insulating film 39. EL layers later formed are extremelythin, and therefore there are cases in which light emission defects arecaused by the existence of the steps. Consequently, it is preferable toperform planarization before forming the pixel electrodes so as to formthe EL layers as planar as possible.

Further, reference numeral 40 denotes a pixel electrode (correspondingto an anode of the EL element) made from a transparent conductive film.After opening a contact hole in the second interlayer insulating film 39and in the first passivation film 38, the pixel electrode 40 is formedso as to be connected to the drain wiring 37 of the current controllingTFT 202 in the formed opening portion.

A conductive thin film made of a chemical compound of indium oxide andtin oxide is used as the pixel electrode in this embodiment mode.Further, a small amount of gallium may also be added. In addition, achemical compound of indium oxide and zinc oxide can also, be used.

Then, an organic resin film of an organic resin is formed on the pixelelectrode by spin coating so as to fill up the electrode hole 46 on thepixel electrode. Note that, in this case, an acrylic resin is used asthe organic resin film.

Further, although the organic resin film of an organic resin is formedon the pixel electrode, an insulator, which can be an insulating filmmay also be used. Note that, as the insulator, an inorganic materialcontaining silicon such as silicon oxide, oxidized silicon nitride, orsilicon nitride may be used.

After the acrylic resin is formed on the whole surface, exposure tolight is performed using a resist mask and etching is performed to formthe protective portions 41 a and 41 b illustrated in FIG. 2.

The protective portion 41 b is the portion of the pixel electrode wherethe electrode hole is filled up with the acrylic resin. The protectiveportion 41 a is provided in a space between pixel electrodes. A spacebetween pixel electrodes is a portion where no pixel electrode is formedin a pixel portion having a plurality of pixel electrodes formedtherein, for example, a portion between pixel electrodes, etc. Whenetching is performed to form a protective portion, if the materialforming the second interlayer insulating film between the pixelelectrodes is the material forming the protective portion, there is apossibility in that the second interlayer insulating film is alsosimultaneously etched.

Note that the thickness of a rising portion in cross section of theprotective portions 41 a and 41 b from the pixel electrode is 0.1 to 1μm, preferably 0.1 to 0.5 μm, more preferably 0.1 to 0.3 μm.

Though a case where an acrylic resin is used as the organic resin forforming the protective portions 41 a and 41 b is described, the materialmay be a polyimide resin, a polyamide resin, or a resin containing ahigh molecular compound of siloxane such as CYCLOTEN. Further, theviscosity of such an organic resin used is preferably 10⁻³ Pa·s to 10⁻¹Pa·s.

By providing the protective portion 41 b and filling up the electrodehole with the organic resin as in the above, the problem of the shortcircuit between the pixel electrode 40 (anode) and the cathode 43 causedwhen the EL layer 42 is disconnected, can be solved.

A method of manufacturing the protective portion 41 b is now describedwith reference to FIG. 4.

FIG. 4A illustrates the protective portion 41 b formed by patterningafter the organic resin film is formed on the pixel electrode 40. Dadenotes the thickness of the organic resin film. When the thickness isthin, a cavity, develops in an upper portion as in the protectiveportion 41 b of FIG. 4A.

The extent of the cavity depends on the tapered angle of the electrodehole and on the thickness of the organic resin film. If the thickness ofthe organic resin film is extremely thin, there is a fear that theelectrode hole can not be filled up completely and the organic resinfilm can not act as the protective portion.

On the other hand, if the thickness of the organic resin film is thick,a step is again generated.

As a method of solving this problem, as illustrated in FIG. 4B, afterthe organic resin film is formed at the thickness of Db, the protectiveportion 41 b is formed by patterning, and further, the whole surface isetched to make the thickness to be Da. This makes it possible to formthe protective portion 41 b with a planarized upper portion and anappropriate thickness as illustrated in FIG. 4C.

However, if the method illustrated in FIG. 4B is used, the pixelelectrode exposed to the surface when the protective portion 41 b isetched after being patterned is also subject to the etching. FIG. 5illustrates a manufacturing method taking this point into consideration.

First, as illustrated in FIG. 5A, the organic resin film is formed atthe thickness of Db on the pixel electrode 40. Then, the whole surfaceis etched to make the thickness to be Da. Further, patterning isperformed to form the protective portion 41 b.

With regard to the protective portion 41 b, it may be formed bypatterning after the organic resin is formed as illustrated in FIG. 4A,or, it may be formed by etching the whole surface after patterning asillustrated in FIG. 4B. Further, as illustrated in FIG. 5A, it may beformed by patterning after the whole surface is etched.

As illustrated in FIG. 5, the outer diameter Rb of the protectiveportion 41.b and the inner diameter Ra of the electrode hole 46 have arelationship of Rb>Ra. Note that the protective portion 41 b describedwith reference to FIG. 4 or FIG. 5 has the structure illustrated in FIG.5C. More specifically, a solid line of 41 a in FIG. 5C represents theouter diameter of the protective portion 41 b, while a broken line of 41b in FIG. 5C represents the inner diameter of the electrode hole 46.

Then, the EL layer 42 is formed. Here, a method of forming the EL layerby spin coating a high molecular organic EL material dissolved in asolvent is described. Note that, though a description will be made of acase, as an example, where a high molecular organic EL material is usedas the organic EL material for forming the EL layer, a low molecularweight organic EL material may also be used.

Polyparaphenylene vinylene (PPV), polyvinyl carbazole (PVK) andpolyfluorane can be given as typical high molecular organic materials.

Note that there are various types of PPV organic EL materials, and forexample, chemical formulae such as those below have been reported. (SeeH. Shenk, H. Becker, O. Gelsen, E. Kluge, W. Kreuder, and H. Spreitzer,“Polymers for Light Emitting Diodes,” Euro Display, Proceedings, 1999,pp. 33-7.)

Further, polyphenylvinyl having the chemical formula disclosed inJapanese Patent Application Laid-open No. Hei 10-92576 can also be used.The chemical formula is as below.

In addition, as a PVK organic EL material, the following chemicalformula is included therein.

The polymer organic EL material can be coated while dissolving thematerial in a solvent as a polymer. Also, the material can bepolymerized after dissolving it in a solvent as a monomer and coatingit. When coating it in a monomer state, first a polymer precursor isformed. By heating it within a vacuum, polymerization is effected toform a polymer.

As specific EL layers, cyano-paraphenylene vinylene may be used in a redcolor light emitting EL layer; polyphenylene vinylene may be used in agreen light emitting EL layer; and polyphenylene vinylene orpolyalkylphenylene may be used in a blue color light emitting EL layer.The film thickness may be set from 30 to 150 nm (preferably between 40and 100 nm).

Note that the above materials are exemplified as one example of organicEL materials which can be used as EL layers in the present invention,thereby being not necessary to limit the materials to those.

Also, toluene, xylene, chlorobenzene, dichlorobenzene, anisole,chloroform, dichloromethane, ā-butylractone, butyl-cell-solve,cyclohexane, NMP (N-methyl-2-piloridon), cyclohexanone, dioxane, and THF(tetrahydrofluorane) are exemplified as typical solvents.

In addition, the EL layer 42 easily degrades in accordance with theexistence of hydrogen or oxygen when forming the EL layer 42, andtherefore it is preferable to perform film formation within an inertgas, such as nitrogen or argon, as an atmosphere having little hydrogenand oxygen for the process environment. In addition, an environment ofthe solvent used in the coating process may also be used as the processatmosphere because the vaporization speed of the solvent, in which an ELmaterial is dissolved, may be controlled. Note that, in order to performfilm formation of the light emitting layers within this atmosphere, itis preferable that the thin film formation apparatus of FIG. 1 may beplaced in a clean booth filled with an inert gas.

Also, with regard to the method of forming the EL layer, other than spincoating described here, ink jetting or the like may be employed.

Further, in case that the EL layer is formed of a low molecular weightorganic EL material, vapor deposition or the like may also be used. Notethat, as the low molecular weight organic EL material, known materialscan be used.

After forming the EL layer 42 as above, a cathode 43 made from a shadingconductive film, a protective electrode 44, and a second passivationfilm 45 are formed next. A conductive film made from MgAg is used as thecathode 43 in this embodiment mode, and a conductive film made fromaluminum is used as the protective electrode 44. Further, a siliconnitride film having a thickness of 10 nm to 1 μm (preferably between 200and 500 nm) is used as a second passivation film 45.

Note that the EL layers are weak with respect to heat as stated above,and therefore it is preferable to perform film formation of the cathode43 and the second passivation film 45 at as low a temperature aspossible (preferably in the range from room temperature to 120° C.). Itcan therefore be said that plasma CVD, vacuum evaporation, and solutioncoating (spin coating) are desirable as the film deposition methods.

That which is thus completed is referred to as an active matrixsubstrate, and an opposing substrate (not shown) is formed opposing theactive matrix substrate. A glass substrate is used as the opposingsubstrate in this embodiment mode. Note that a substrate made fromplastic or ceramic may also be used as the opposing substrate.

Further, the active matrix substrate and the opposing substrate arejoined by a sealant (not shown), with the result that an airtight space(not shown) is formed. The airtight space is filled with argon in thisembodiment mode. It is also possible, of course, to arrange a dryingagent such as barium oxide and to arrange an oxidation preventing agentwithin the airtight space.

Further, by forming a film of a metal having a low work function andliable to be oxidized or of a hygroscopic metal on the surface of anopposing substrate on the side of the active matrix substrate, afunction to capture oxygen or a hygroscopic function can be provided.Note that, if such a metal film is formed after unevenness is producedon the opposing substrate with an organic resin such as a photosensitiveacrylic resin, the surface area can be made larger, which is moreeffective.

EMBODIMENTS Embodiment 1

A method of simultaneously forming a TFT in a pixel portion and a TFT ina driver circuit portion provided on the periphery thereof in accordancewith an embodiment of the present invention is now described withreference to FIGS. 6 to 8. Note that, for the sake of simplicity of thedescription, with regard to the driver circuit, only a CMOS circuit as abasic circuit is illustrated.

First, as illustrated in FIG. 6A, a base film 301 is formed at thethickness of 300 nm on a glass substrate 300. In this embodiment, as thebase film 301, a silicon oxynitride film at the thickness of 100 nm anda silicon oxynitride film at the thickness of 200 nm laminated theretoare used. In this case, the concentration of nitrogen of the film incontact with the glass substrate 300 is preferably 10 to 25 wt %. Ofcourse, an element may be directly formed on a quartz substrate withoutproviding such a base film.

Then, an amorphous silicon film (not shown) at the thickness of 50 nm isformed on the base film 301 by a known film formation method. Note thatthe film formed here is not limited to the amorphous silicon film, andmay be a semiconductor film containing amorphous structure (including amicrocrystal semiconductor film). Further, the film may be a compoundsemiconductor film containing amorphous structure such as an amorphoussilicon germanium film. The film thickness is preferably 20 to 100 nm.

Then, the amorphous silicon film is crystallized by a known technologyto form a crystal silicon film (also referred to as a polycrystalsilicon film or a polysilicon film) 302. The known crystallizingtechnology includes thermal crystallization using an electric furnace,laser anneal crystallization using a laser light, and lamp annealcrystallization using infrared light. In this embodiment, an excimerlaser light using XeCl gas is used to perform the crystallization.

Note that, though a pulse oscillation type excimer laser light processedto be linear is used in this embodiment, the laser light may berectangular. Also, a continuous oscillation type argon laser light or acontinuous oscillation type excimer laser light may be used.

Though a crystal silicon film is used as the active layer of the TFTs inthis embodiment, an amorphous silicon film may also be used. Further, itmay be that the active layer switching TFT, which is required to lowerthe off current is formed of an amorphous silicon film, and the activelayer of the electric current controlling TFT is formed of a crystalsilicon film. Since the carrier mobility of the amorphous silicon filmis low, it conducts less electric current, and thus, off current is lessliable to flow. Therefore, both the advantage of an amorphous siliconfilm, which conducts less electric current and the advantage of acrystal silicon film, which conducts more electric current, can beutilized.

Then, as illustrated in FIG. 6B, a protective film 303 of a siliconoxide film is formed at the thickness of 130 nm on the crystal siliconfilm 302. The thickness of the protective film 303 may be selected fromthe range of 100 to 200 nm (preferably 130 to 170 nm). The protectivefilm 303 may be any insulating film containing silicon. The protectivefilm 303 is provided so that, when impurity is doped, the crystalsilicon film is not directly exposed to plasma and that preciseconcentration control is made possible.

Then, resist masks 304 a and 304 b are formed on the protective film303, and an impurity element imparting n-type (hereinafter referred toas n-type impurity element) is doped through the protective film 303. Asthe n-type impurity element, representatively, an element belonging to agroup 15, typically phosphorus or arsenic can be used. Note that, inthis embodiment, phosphorus is doped at the concentration of 1×10¹⁸atoms/cm³ by plasma (ion) doping using plasma excited phosphine (PH₃)without mass separation. Of course, ion implantation with massseparation may also be used.

The dose is controlled such that the n-type impurity element iscontained in an n-type impurity region 305 formed in this process at theconcentration of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ (representatively 5×10¹⁷ to5×10¹⁸ atoms/cm³).

Then, as illustrated in FIG. 6C, the protective film 303 and the resistmasks 304 a and 304 b are removed, and the added element belonging tothe group 15 is activated. The activation may be performed using a knowntechnology. In this embodiment, the activation is performed byirradiation of an excimer laser light. Of course, the excimer laserlight may be a pulse oscillation type and may be a continuousoscillation type, and the method for activation is not limited to theexcimer laser light. However, since the object is to activate the dopedimpurity element, energy irradiation to an extent with which the crystalsilicon film is not melted is preferable. Note that the laser light maybe irradiated without removing the protective film 303.

Note that the activation of the impurity element with the laser lightmay be made together with activation with heat treatment. In case thatsuch activation with heat treatment is performed, taking intoconsideration the heat resistance of the substrate, heat treatment isperformed preferably at about 450 to 550° C.

This process clarifies an end portion of the n-type impurity region 305,that is, a boundary portion (junction portion) between the n-typeimpurity region 305 and the region around the n-type impurity region 305with no n-type impurity element doped therein. This means that, at atime when the TFT is completed later, an LDD region and a channelforming region can form a very satisfactory junction portion.

Then, as illustrated in FIG. 6D, unnecessary portions of the crystalsilicon film are removed to form island-like semiconductor films(hereinafter referred to as active layers) 306 to 309.

Then, as illustrated in FIG. 6E, a gate insulating film 310 is formed soas to cover the active layers 306 to 309. As the gate insulating film310, an insulating film containing silicon at the thickness of 10 to 200nm, preferably 50 to 150 nm is used. The film 310 may be of a singlelayer structure or may be of a laminated structure. In this embodiment,a silicon oxynitride film at the thickness of 110 nm is used.

Then, a conductive film at the thickness of 200 to 400 nm is formed andpatterned to form gate electrodes 311 to 315. The end portions of thegate electrodes 311 to 315 may be tapered. Note that, in thisembodiment, the material of the gate electrodes are different from thematerial of wirings for leading which are electrically connected to thegate electrodes (hereinafter referred to as gate wirings). Morespecifically, the material of the gate wirings has lower resistance thanthat of the material of the gate electrodes. This is for the purpose ofusing a material which can be precisely processed for the gateelectrodes and of using a material which may not be precisely processedbut which has low resistance for the gate wirings. Of course, the gateelectrodes and the gate wirings may be formed of the same material.

Though the gate electrodes may be formed of a single layer conductivefilm, they are preferably formed of a laminated film having, forexample, two layers or three layers as necessity requires. The materialof the gate electrode may be any known conductive film. However,preferably, as described in the above, the material can be preciselyprocessed. More specifically, it is preferable that the material can bepatterned to have the line width of 2 μm or less.

Representatively, a film formed of an element selected from the groupconsisting of tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chromium (Cr), and silicon (Si), a film formed of a nitride of theabove elements (representatively, a tantalum nitride film, a tungstennitride film, or a titanium nitride film), a film formed of an alloy ofthe above elements (representatively Mo—W alloy or Mo—Ta alloy), or afilm formed of a silicide of the above elements (representatively, atungsten silicide film or a titanium silicide film) can be used. Ofcourse, these films may be used as a single layer or may be laminated.

In this embodiment, a laminated film formed of a tantalum nitride (TaN)film at the thickness of 50 nm and a tantalum (Ta) film at the thicknessof 350 nm is used. This film may be formed by sputtering. By adding as asputtering gas an inert gas such as Xe or Ne, peeling off of the filmdue to stress can be prevented.

Further, in this case, the gate electrode 312 is formed so as to overlapa part of the n-type impurity region 305 while sandwiching the gateinsulating film 310. This overlap portion becomes an LDD region later,which overlaps the gate electrode. Note that, though the gate electrodes313 and 314 appear to be separated in section, they are actuallyelectrically connected to each other.

Then, as illustrated in FIG. 7A, an n-type impurity element (phosphorusin this embodiment) is doped in a self-aligning manner using as masksthe gate electrodes 311 to 315. Control is made so that theconcentration of phosphorus doped in impurity regions 316 to 323 formedin this way is ½ to 1/10 (representatively, ⅓ to ¼) of that in then-type impurity region 305. More specifically, it is preferable that theconcentration is 1×10¹⁶ to 5×10¹⁸ atoms/cm³ (typically, 3×10¹⁷ to 3×10¹⁸atoms/cm³).

Then, as illustrated in FIG. 7B, resist masks 324 a to 324 d are formedso as to cover the gate electrodes and the like, and an n-type impurityelement (phosphorus in this embodiment) is doped to form impurityregions 325 to 329 containing phosphorus at a high concentration. Inthis case, too, ion doping using phosphine (PH₃) is performed. Controlis made so that the concentration of phosphorus in this region is 1×10²⁰to 1×10²¹ atoms/cm³ (representatively, 2×10²⁰ to 5×10²¹ atoms/cm³).

This process forms a source region and a drain region of an n-channeltype TFT. However, with regard to the switching TFT, part of the n-typeimpurity regions 319 to 321 formed in the process of FIG. 7A are left.The left regions correspond to LDD regions 15 a to 15 d, respectively,of the switching TFT 201 of in FIG. 2.

Then, as illustrated in FIG. 7C, the resist masks 324 a to 324 d areremoved, and a resist mask 332 is newly formed. Then, a p-type impurityelement (boron in this embodiment) is doped to form impurity regions 333to 336 containing boron at a high concentration. In this case, boron isdoped by ion doping using diborane (B₂H₆) such that the concentration is3×10²⁰ to 3×10²¹ atoms/cm³ (representatively, 5×10²⁰ to 1×10²¹atoms/cm³).

Note that, while phosphorus has already been doped in the impurityregions 333 to 336 at the concentration of 1×10²⁰ to 1×10²¹ atoms/cm³,the concentration of boron doped in this process is at least three timesas much as that of phosphorus. Therefore, the n-type impurity regionspreviously formed are completely reversed to a p-type, and function asp-type impurity regions.

Then, after the resist mask 332 is removed, the n-type and p-typeimpurity elements doped at their respective concentrations areactivated. The activation can be performed by furnace annealing, laserannealing, or lamp annealing. In this embodiment, heat treatment in anitrogen atmosphere at 550° C. for four hours is performed in anelectric furnace.

In this case, it is important to remove oxygen in the atmosphere as muchas possible. This is because, if any oxygen exists at all, the surfacesof the exposed gate electrodes are oxidized, which leads to increasedresistance and difficulty in forming an ohmic contact later.Accordingly, it is desirable that the concentration of oxygen in theprocessing atmosphere in the above activation process is 1 ppm or less,preferably 0.1 ppm or less.

After the activation process is completed, a gate wiring 337 at thethickness of 300 nm is formed as illustrated in FIG. 7D. The material ofthe gate wiring 337 may be a metal containing as a main componentaluminum (Al) or copper (Cu) (the percentage is 50 to 100% as acomposition). With regard to the arrangement, as illustrated in FIG. 3,the gate wiring is formed such that the gate wiring 211 is electricallyconnected to gate electrodes 19 a and 19 b (313 and 314 of FIG. 6E) ofthe switching TFT.

With taking such a structure, the wiring resistance of the gate wiringcan be made extremely small, and therefore, an image display region(pixel portion) having a large area can be formed. More specifically,the pixel structure according to the present example is extremelyeffective in realizing an EL display device having a screen the diagonalsize of which is 10 inches or larger (and further, 30 inches or larger).

Then, as illustrated in FIG. 8A, a first interlayer insulating film 338is formed. As the first interlayer insulating film 338, a single layerinsulating film containing silicon, or a laminated film which is acombination of two or more kinds of insulating films containing siliconmay be used. Also, the film thickness may be 400 nm to 1.5 μm. In thisembodiment, it may employ a structure in which a silicon oxide film atthe thickness of 800 nm is laminated on a silicon oxynitride film at thethickness of 200 nm.

Further, heat treatment at 300 to 450° C. for one to twelve hours isperformed in an atmosphere containing 3 to 100% of hydrogen to performhydrogenation. This process is a process where dangling bonds in thesemiconductor film are terminated by hydrogen using thermally excitedhydrogen. The hydrogenation may also be performed by plasmahydrogenation (using plasma hydrogen).

Note that the hydrogenation may be performed during the first interlayerinsulating film 338 is formed. More specifically, the abovehydrogenation may be performed after the silicon oxynitride film at thethickness of 200 nm is formed and before the silicon oxide film at thethickness of 800 nm is formed.

Then, contact holes are formed in the first interlayer insulating film338 and the gate insulating film 310, and source wirings 339 to 342 anddrain wirings 343 to 345 are formed. Note that, in this embodiment, theelectrodes are laminated films having a three-layer structure formed bycontinuously forming by sputtering a Ti film at the thickness of 100 nm,an aluminum film containing Ti at the thickness of 300 nm, and a Ti filmat the thickness of 150 nm. Of course, other conductive films may alsobe used.

Subsequently, a first passivation film 346 at the thickness of 50 to 500nm (representatively 200 to 300 nm) is formed. In this embodiment, asilicon oxynitride film at the thickness of 300 nm is used as the firstpassivation film 346. Instead of the silicon oxynitride film, a siliconnitride film may be used.

Note that plasma treatment using gas containing hydrogen such as H₂ orNH₃ prior to the formation of the silicon oxynitride film is effective.By supplying hydrogen excited by this pretreatment to the firstinterlayer insulating film 338, and by performing heat treatment, thequality of the first passivation film 346 is improved. At the same time,hydrogen doped in the first interlayer insulating film 338 is diffusedto the lower layer side. Therefore, the active layers can behydrogenated effectively.

Then, as illustrated in FIG. 8B, a second interlayer insulating film 347of an organic resin is formed. As the organic resin, a polyimide resin,a polyamide resin, an acrylic resin, or a resin containing a highmolecular compound of siloxane can be used. In particular, since thesecond interlayer insulating film 347 is more expected to perform theplanarization, an acrylic resin which is excellent in planarity ispreferable. In this embodiment, an acrylic resin film is formed at athickness with which a step formed by the TFTs is sufficientlyplanarized. Preferably, the thickness of the acrylic resin is 1 to 5 μm(more preferably, 2 to 4 μm).

Then, a contact hole is formed in the second interlayer insulating film347 and the first passivation film 346, and a pixel electrode 348electrically connected to the drain wiring 345 is formed. In thisembodiment, an indium tin oxide (ITO) film is formed at the thickness of110 nm, and is patterned to form the pixel electrode. A transparentconductive film of indium oxide with 2 to 20% of zinc oxide (ZnO) mixedtherewith may also be used. This pixel electrode becomes the anode ofthe EL element.

Then, as illustrated in FIG. 8C, protective portions 349 a and 349 b ofan organic resin are formed. The protective portions 349 a and 349 b maybe formed by patterning a resin film such as an acrylic resin film or apolyimide film at the thickness of 1 to 2 μm. As illustrated in FIG. 3,the protective portions 349 a and 349 b are formed in a space betweenpixel electrodes and in an electrode hole, respectively.

Then, an EL layer 350 is formed. More specifically, an organic ELmaterial which becomes the EL layer 350 is dissolved in a solvent suchas chloroform, dichloromethane, xylene, toluene, tetrahydrofuran, orN-methylpyrrolidone, and is applied by spin coating. Then, the solventis volatilized by heat treatment. In this way, the film of the organicEL material (EL layer) is formed.

In this embodiment, after the EL material is formed at the thickness of80 nm, heat treatment for one to five minutes is performed using a hotplate at 80 to 150° C. to volatize the solvent.

Note that a known material can be used as the EL material. Taking intoconsideration the driving voltage, such a known material is preferablyan organic material. Note that, since the EL layer 350 is of a singlelayer structure in this embodiment, it may be of a laminated structurehaving an electron injection layer, an electron transmission layer, ahole transmission layer, a hole injection layer, an electron blocklayer, or a hole element layer as necessity requires. Further, though,in this embodiment, a case where an MgAg electrode is used as a cathode351 of the EL element is described, other known materials may also beused.

After the EL layer 350 is formed, the cathode (MgAg electrode) 351 isformed by vacuum evaporation. Note that the thickness of the EL layer350 is preferably 80 to 200 nm (typically 100 to 120 nm) and thethickness of the cathode 351 is preferably 180 to 300 nm (typically 200to 250 nm).

Further, a protective electrode 352 is provided on the cathode 351. Asthe protective electrode 352, a conductive film containing as the maincomponent aluminum may be used. The protective electrode 352 may beformed by vacuum evaporation using a mask.

Finally, a second passivation film 353 of a silicon nitride film isformed at the thickness of 300 nm. Though, actually, the protectiveelectrode 352 protects the EL layer from moisture and the like, byfurther forming the second passivation film 353, the reliability of theEL element can be further enhanced.

In case of the present embodiment, as illustrated in FIG. 8C, the activelayer of the n-channel type TFT 205 includes a source region 355, adrain region 356, an LDD region 357, and a channel forming region 358.The LDD region 357 overlaps the gate electrode 312 while sandwiching thegate insulating film 310.

The LDD region is formed only on the side of the drain region, so as notto lower the operation speed. Further, with regard to the n-channel typeTFT 205, it is not necessary to consider the off current, and theoperation speed is more important. Therefore, it is desirable that theLDD region 357 is completely covered with the gate electrode to make theresistance component as small as possible. In other words, it ispreferable that there is no so-called offset.

In this way, the active matrix substrate having the structure asillustrated in FIG. 8C is completed.

By the way, by arranging most appropriately structured TFTs not only inthe pixel portion but also in the driver circuit portion, an activematrix substrate according to the present embodiment is extremelyreliable, and its operation characteristics can be improved.

First, a TFT structured to decrease hot carrier injection so as not tolower the operation speed as much as possible is used as the n-channeltype TFT 205 of the CMOS circuit for forming the driver circuit portion.Note that the driver circuit as referred herein includes a shiftregister, a buffer, a level shifter, and a sampling circuit (asample-and-hold circuit). In case digital driving is performed, a signalconversion circuit such as a D/A converter may be included.

Note that, among driver circuits, a sampling circuit is different alittle from other circuits and a large amount of current bidirectionallyflows through the channel forming region. In other words, the functionof the source region and the function of the drain region are reversed.Further, it is necessary to suppress the off current value as much aspossible. In this sense, it is desirable that a TFT having a functionwhich is between the function of the switching TFT and the function ofthe electric current controlling TFT, is arranged.

Accordingly, it is desirable that, as the n-channel type TFT forming thesampling circuit, a TFT structured as illustrated in FIG. 9 is arranged.As illustrated in FIG. 9, parts of LDD regions 901 a and 901 b overlap agate electrode 903 through a gate insulating film 902. The purpose is totake measures against deterioration due to hot carrier injection causedwhen electric current flows therethrough. The case of the samplingcircuit is different from other cases in that such LDD regions areprovided on both sides so as to sandwich a channel forming region 904.

Note that, actually, after the process illustrated in FIG. 8C iscompleted, the device is preferably packaged (enclosed) in a coveringmaterial such as airtight glass, quartz, or plastic so that the deviceis not exposed to the outside air. In this case, a hygroscopic agentsuch as barium oxide or an antioxidant is preferably disposed inside thecovering material.

Further, after the airtightness is enhanced by processing such as thepackaging, a connector (flexible print circuit: FPC) for connectingterminals led from elements or circuits formed on the substrate toexternal signal terminals is attached to complete the device as aproduct. The device in this state, i.e., in a shippable state is hereinreferred to as an EL display device (or EL module).

Here, the structure of the active matrix EL display device according tothe present embodiment is described with reference to a perspective viewof FIG. 10. The active matrix EL display device according to the presentembodiment includes a pixel portion 602, a gate side driver circuit 603,and a source side driver circuit 604 formed on a glass substrate 601. Aswitching TFT 605 in the pixel portion is an n-channel type TFT, and isdisposed at an intersection of a gate wiring 606 connected to the gateside driver circuit 603 and a source wiring 607 connected to the sourceside driver circuit 604. A drain of the switching TFT 605 is connectedto a gate of an electric current controlling TFT 608.

Further, a source side of the electric current controlling TFT 608 isconnected to a power supply line 609. In a structure of this embodiment,the power supply line 609 has a ground potential (an earth potential).Further, a drain of the electric current controlling TFT 608 isconnected to an EL element 610. A given voltage (3 to 12 V, preferably 3to 5 V) is applied to an anode of the EL element 610.

Further, an FPC 611 that becomes an external input/output terminal isprovided with connection wirings 612 and 613 for transmitting a signalto a driver circuit portion, and a connection wiring 614 connected tothe power supply line 609.

Also, FIG. 11 illustrates an example of a circuit structure of the ELdisplay device illustrated in FIG. 10. The EL display device accordingto the present embodiment has a source side driver circuit 801, a gateside driver circuit (A) 807, a gate side driver circuit (B) 811, and apixel portion 806. Note that the driver circuit portion as used hereinis a generic name, and includes the source side driver circuit and thegate side driver circuit.

The source side driver circuit 801 is provided with a shift register802, a level shifter 803, a buffer 804, and a sampling circuit(sample-and-hold circuit) 805. Further, the gate side driver circuit (A)807 is provided with a shift register 808, a level shifter 809, and abuffer 810. The gate side driver circuit (B) 811 is similarlystructured.

In this case, the driving voltage of the shift registers 802 and 808 is5 to 16 V (representatively 10 V). For an n-channel type TFT used in aCMOS circuit that constructs the circuit, the structure denoted as 205in FIG. 8C is suitable.

Similarly to the case of the shift registers, for the level shifters 803and 809 and the buffers 804 and 810, a CMOS circuit including then-channel type TFT 205 illustrated in FIG. 8C is suitable. Note that tomake the gate wirings have a multi-gate structure such as a double-gatestructure or a triple-gate structure is effective in improving thereliability of the respective circuits.

In addition, with regard to the sampling circuit 805, since the sourceregion and the drain region are reversed and, in addition, it isnecessary to lower the off current value, a CMOS circuit including ann-channel type TFT 208 illustrated in FIG. 9 is suitable.

Also, in the pixel portion 806, pixels structured as illustrated in FIG.2 are arranged.

Note that the above structure can be easily materialized bymanufacturing the TFTs according to the manufacturing processillustrated in FIGS. 6 to 8. Further, though only the structure of thepixel portion and the driver circuit portion are illustrated in thisembodiment, according to the manufacturing process of the presentembodiment, logic circuits other than the driver circuit such as asignal division circuit, a D/A converter circuit, an operationalamplifier circuit, and a γ correction circuit can also be formed on thesame substrate. Further, it is expected that a memory unit, amicroprocessor, and the like can also be formed.

Further, the EL module according to the present embodiment including acovering material is described with reference to FIGS. 12A and 12B. Thereference numerals used in FIGS. 10 and 11 are also used here asnecessity requires.

FIG. 12A is a top view illustrating a state illustrated in FIG. 10 witha sealing structure provided therewith. 602, 603, and 604 shown bydashed lines denote a pixel portion, a gate side diver circuit, and asource side driver circuit, respectively. The sealing structureaccording to the present invention is a structure provided with afilling agent (not shown), a covering material 1101, a sealing material(not shown), and a frame material 1102 for the state illustrated in FIG.10.

Here, FIG. 12B is a sectional view taken along the line A-A′ of FIG.12A. Note that like reference numerals denote like parts in FIGS. 12Aand 12B.

As illustrated in FIG. 12B, the pixel portion 602 and the gate sidedriver circuit 603 are formed on the substrate 601. The pixel portion602 is formed of a plurality of pixels including the electric currentcontrolling TFT 202 and the pixel electrode 348 electrically connectedthereto. The gate side driver circuit 603 is formed using a CMOS circuitwhere the n-channel type TFT 205 and the p-channel type TFT 206 arecomplementarily combined.

The pixel electrode 348 functions as an anode of the EL element. Also,the protective film 349 a is formed at both ends of the pixel electrode348. The EL layer 350 and the cathode 351 are formed on the protectivefilm 349 a. Further, the protective electrode 352 and the secondpassivation film 353 are formed thereon. As described in the aboveEmbodiment Mode, the structure of the EL element may be reversed and thepixel electrode may be the cathode.

In this embodiment, the protective electrode 352 also functions as awiring, which is common to all the pixels, and is electrically connectedto the FPC 611 via the connection wiring 612. Further, all elementsincluded in the pixel portion 602 and the gate side driver circuit 603are covered with the second passivation film 353. Though the secondpassivation film 353 may be omitted, it is preferable to provide it soas to block the respective elements from the external.

Then, a filling agent 1103 is provided so as to cover the EL elements.The filling agent 1103 also functions as adhesive for adhering thecovering material 1101. As the filling agent 1103, PVC (polyvinylchloride), an epoxy resin, a silicone resin, PVB (polyvinyl butyral), orEVA (ethylene vinyl acetate) can be used. It is preferable to provide ahygroscopic agent (not shown) inside the filling agent 1103, because thehygroscopic effect can be maintained. In this case, the hygroscopicagent may be one added to the filling agent, or may be one enclosed inthe filling agent.

Further; in this embodiment, as the covering material 1101, glass,plastic, or ceramics can be used. Note that to add in advance ahygroscopic agent such as barium oxide inside the filling agent 1103 iseffective.

Then, after the covering material 1101 is adhered using the fillingagent 1103, the frame material 1102 is attached so as to cover the sidesurfaces (exposed surfaces) of the filling agent 1103. The framematerial 1102 is adhered by a sealing material (which functions asadhesive) 1104. In this case, as the sealing material 1104, though aphoto-curable resin is preferably used, if the heat resistance of the ELlayer permits, a thermosetting resin may also be used. Note that thesealing material 1104 is preferably a material that transmits moistureand oxygen as less as possible. Further, a hygroscopic agent may beadded to the inside of the sealing material 1104.

By encapsulating the EL element in the filling agent 1103 using theabove-mentioned method, the EL element can be completely blocked fromthe external, with the result that substances such as moisture andoxygen which promote deterioration of the EL layer due to oxidation canbe prevented from entering. Accordingly, an EL display device with highreliability can be manufactured.

Embodiment 2

In Embodiment 1, a manufacturing method is described where, after theorganic resin is coated to the whole surface above the pixel electrode,patterning is performed using an exposing unit, the partial protectiveportions are formed where the organic resin fills up the electrode holeand the space between pixel electrodes, and then, the EL layer isformed. However, since there is the exposure process, the throughput isinsufficient. In this embodiment, a method is described where, after anorganic resin is coated to the whole surface above a pixel electrode,without performing patterning, planarization is performed using etchback, and then, portions other than an organic resin filling up anelectrode hole and a space between pixel electrodes, are etched.

Here, FIG. 13 illustrates the structure in cross section of a pixelportion of an EL display device according to the present invention.

FIG. 13A illustrates a pixel electrode 1040 and an electric currentcontrolling TFT which is electrically connected to the pixel electrode1040. After a baser film 1012 is formed on a substrate 1011, theelectric current controlling TFT is formed so as to have an active layerincluding a source region 1031, a drain region 1032, and a channelforming region 1034, a gate insulating film 1018, a gate electrode 1035,a first interlayer insulating film 1020, a source wiring 1036, and adrain wiring 1037. Note that, though the gate electrode 1035 is of asingle-gate structure in the figure, it may be of a multi-gatestructure.

Then, a first passivation film 1038 is formed at the thickness of 10 nmto 1 μm (preferably 200 to 500 nm). As the material, an insulating filmcontaining silicon (especially, a silicon oxynitride film or a siliconnitride film is preferable) can be used.

A second interlayer insulating film (which may also be referred to asplanarizing film) 1039 is formed on the first passivation film 1038 soas to cover the respective TFTs to planarize a step formed by the TFTs.As the second interlayer insulating film 1039, an organic resin film ofsuch as a polyimide resin, a polyamide resin, an acrylic resin, or aresin containing a high molecular compound of siloxane is preferable. Ofcourse, an inorganic film may also be used if it can perform sufficientplanarization.

It is quite important to planarize, by the second interlayer insulatingfilm 1039, a step formed by the TFTs. Since an EL layer to be formedlater is very thin, existence of a step may cause failure lightemission. Therefore, it is preferable that planarization is performedprior to the formation of the pixel electrode in order to make as planaras possible the surface on which the EL layer is formed.

Further, after a contact hole (an opening) is formed in the secondinterlayer insulating film 1039 and the first passivation film 1038, apixel electrode 1040 (corresponding to an anode of the EL element) of atransparent conductive film is formed so as to be connected at theformed opening to the drain wiring 1037 of the electric currentcontrolling TFT.

In this embodiment, as the pixel electrode, a conductive film formed ofa compound of indium oxide and tin oxide is used. A small amount ofgallium may be doped into the compound. Further, a compound of indiumoxide and zinc oxide may be used.

Then, an organic resin film 1041 of an organic resin is formed on thepixel electrode. As the organic resin, though materials such as apolyamide resin, a polyimide resin, an acrylic resin, and a resincontaining a high molecular compound of siloxane may be used, here, anacrylic resin such as acrylic ester resin, acrylate resin, methacrylicacid ester resin, or methacrylic acid resin is used.

Note that a resin containing a high molecular compound of siloxaneincludes CYCLOTEN.

Further, though, in this case, the organic resin film of an organicresin is formed on the pixel electrode, an insulator which can be aninsulating film may be used.

As the insulator, an insulating film containing silicon such as siliconoxide, silicon oxynitride, or silicon nitride may be used.

The thickness (Dc) of the organic resin film 1041 is preferably 0.1 to 2μm, and more preferably, 0.2 to 0.6 μm.

After the organic resin film 1041 is formed, the whole surface of theorganic resin film 1041 is etched until Dc=0 is attained. At that point,the etching is completed. In this way, the acrylic resin filling up theelectrode hole is left to form a protective portion 1041 b.

Note that, as the etching method, dry etching is preferable. First,etching gas suitable for the organic resin material to be etched isintroduced into a vacuum chamber. Thereafter, high frequency voltage isapplied to an electrode to generate plasma of the etching gas.

In the plasma of the etching gas, charged particles such as positiveions, negative ions, and electrons, and neutral active species existscatteringly. When the etching species are adsorbed by the etchedmaterial, chemical reaction is caused on the surface, and an etchingproduct is generated. By removing the etching product, the etching isperformed.

Further, when an acrylic resin is used as the material of the protectivefilm, preferably the etching gas containing oxygen as the main componentis used.

Note that, in this embodiment, etching gas made of oxygen, helium, andcarbon tetrafluoride (CF₄) is used as the etching gas containing oxygenas the main component. As other materials, gas containing fluorocarbonsuch as carbon hexafluoride may be used.

Note that, in those etching gases, it is preferable that oxygen is 60%or more of the whole etching gas.

As illustrated in this embodiment, after the organic resin film isformed on the pixel electrode by spin coating, the whole surface isetched in the direction shown by arrows in FIG. 13B so that a protectiveportion 1041 b is formed in an electrode hole 1046. Note that, asillustrated in FIG. 13B, an exposed surface of the protective portion1041 b formed here is flush with an exposed surface of the pixelelectrode 1040.

Note that the etching rate is examined in advance, and the etching timeis set such that the etching ends just when the organic resin film onthe pixel electrode 1040 is removed except the protective portion 1041b. In this way, the upper surface of the pixel electrode 1040 is flushwith the upper surface of the protective portion 1041 b.

Further, when these organic resins are used, the viscosity of theorganic resin is preferably 10⁻³ Pa·s to 10⁻¹ Pa·s.

After the protective portion 1041 b is formed, as illustrated in FIG.13C, an EL material dissolved in a solvent is applied by spin coating toform an EL layer 1042.

After the EL layer 1042 is formed, a cathode 1043 and a protectiveelectrode 1044 are further formed.

By forming the structure illustrated in FIG. 13C as in the above, theproblem of the short circuit between the pixel electrode 1040 and thecathode 1043 caused when the EL layer 1042 is disconnected at a stepportion in the electrode hole can be solved.

FIG. 13D is a top view in case that the protective portion 1041 b on thepixel electrode 1040 is in the same shape as that of the electrode hole1046 as described in this embodiment.

Further, the structure of the present embodiment can be freely combinedwith the structure of Embodiment 1.

Embodiment 3

In Embodiment 2, a method of forming the protective film by etching,that is, an etch back method is described. However, since the etch backmethod may be inappropriate depending on the kind of the protectivefilm, and the range which can be planarized by the etch back method islimited from several μm to several tens μm, formation of a protectiveportion using chemical mechanical polishing (CMP) is also considered.Such a method is now described also with reference to FIG. 13.

In this embodiment, after the organic resin film 1041 is formed at thethickness of Dc (>0) as illustrated in FIG. 13A of Embodiment 2, theorganic resin film 1041 is pressed against a polishing pad extended on asurface plate opposed to the organic resin film 1041 under constantpressure, and abrasive (slurry) is made to flow therebetween with thesubstrate and the surface plate being rotated to polish the organicresin film 1041 until Dc=0 is attained. Using such a method, which isso-called CMP, the protective portion 1041 b is formed.

The slurry used in the CMP is formed by dispersing polishing particlescalled abrasive in an aqueous solution after pH control. It ispreferable that the slurry is changed depending on the polished film.

In this embodiment, since an acrylic resin is used as the polished film,slurry such as one containing silica (SiO₂), one containing ceria(CeO₂), or one containing fumed silica (SiCl₄) is preferably used.However, other slurries such as one containing alumina (Al₂O₃) or onecontaining zeolite may also be used.

Further, since the electric potential (zeta potential) between theliquid and the abrasive (silica particles) in the slurry influences theprocessing accuracy, the zeta potential is required to be controlled byoptimizing the pH value.

When polishing is performed using CMP, it is difficult to ascertain whenthe polishing is to be ended. If too much polishing is performed, eventhe pixel electrode is polished. By forming a film the processing speedof which is extremely slow as a stopper of the CMP, or, by adopting amethod where the relation between the processing time and the processingspeed is clarified in advance by experiment and the CMP is ended whenpredetermined processing time elapses, too much polishing can beprevented.

As described in the above, by using the CMP, the protective portion 1041b can be formed irrespective of the thickness and the kind of thepolished film.

Note that the structure of the present embodiment can be freely combinedwith the structures of Embodiments 1 and 2.

Embodiment 4

In this embodiment, a case where the present invention is used in apassive type (simple matrix type) EL display device is described withreference to FIG. 14.

In FIG. 14, a substrate 1301 is formed of plastic and an anode 1306 isformed of a transparent conductive film. Note that the substrate 1301may be formed of glass, quartz, or the like.

In this embodiment, as the transparent conductive film, a compound ofindium oxide and zinc oxide is formed by vapor deposition. Note that,though not shown in FIG. 14, a plurality of anodes are arranged to bestripe-like in a direction perpendicular to the plane of the figure.

Further, protective portions 1303 according to the present invention areformed so as to fill up spaces between the anodes 1302 arranged to bestripe-like. The protective portions 1303 are formed along the anodes1302 in the direction perpendicular to the plane of the figure. Notethat the protective portions 1303 of the present embodiment may beformed according to the methods described in Embodiments 1 to 3 using asimilar material.

Then, an EL layer 1304 of a high molecular organic EL material isformed. The organic EL material used may be similar to the one describedin Embodiment 1. Since the EL layer is formed along grooves formed bythe protective portions 1303, the EL layer is also arranged to bestripe-like along the direction perpendicular to the plane of thefigure.

After that, though not shown in FIG. 14, a plurality of cathodes andprotective electrodes are arranged to be stripe-like with theirlongitudinal direction being in parallel to the plane of the figure soas to be orthogonal with respect to the anodes 1302. Note that, in thisembodiment, the cathodes 1305 are formed of MgAg by vapor deposition andthe protective electrodes 1306 are formed of an aluminum alloy film byvapor deposition. Further, though not shown in the figure, wirings areled from the protective electrodes 1306 to portions where an FPC is tobe attached later, such that predetermined voltage is applied to theprotective electrodes 1306.

Further, though not shown in the figure, after the protective electrodes1306 are formed, a silicon nitride film may be provided as a passivationfilm.

In this way, EL elements are formed on the substrate 1301. Note that, inthis embodiment, since the lower electrodes are anodes which transmitlight, light emitted from the EL layers 1304 a to 1304 c are radiated tothe lower surface (substrate 1301). However, the structure of the ELelements may be reversed and the lower electrodes may be cathodes whichblock light. In this case, light emitted by the EL layers are radiatedto the upper surface (the side opposite to the substrate 1301).

Then, a ceramic substrate is prepared as a covering material 1307.Though, in the structure of the present embodiment, a ceramic substratewhich blocks light is used, if the structure of the EL elements isreversed as described in the above, of course it is preferable that thecovering material transmits light, and thus, in that case, a substrateformed of plastic, glass, or the like is used.

After the covering material 1307 is thus prepared, the covering material1307 is adhered by a filling agent 1308 with barium oxide being added asa hygroscopic agent (not shown). After that, a frame material 1310 isattached using a sealing material 1309 formed of an ultraviolet curableresin. In this embodiment, stainless steel is used as the frame material1310. Finally, an FPC 1312 is attached through an anisotropic conductivefilm 1311 to complete the passive type EL display device.

Note that the structure of the present embodiment can be freely combinedwith any structures of Embodiments 1 to 3.

Embodiment 5

It is effective to use a silicon substrate (silicon wafer) as asubstrate when an active matrix EL display device is manufacturedaccording to the present invention. When a silicon substrate is used asthe substrate, elements for switching and elements for controllingelectric current which are formed in a pixel portion and elements fordriving which are formed in a driver circuit portion can be formed usinga known technology for manufacturing MOSFETs used in ICs and LSIs.

MOSFETs can form a circuit with extremely small fluctuation, as can beseen in a known IC or LSI. In particular, MOSFETs are effective informing an analog-driven active matrix EL display device, whichrepresents gray scale by the electric current value.

Note that, since the silicon substrate blocks light, it is necessarythat the device is structured such that light from the EL layer isradiated to the side opposite to the substrate. The EL display deviceaccording to the present embodiment is similar in structure to the oneillustrated in FIG. 12, but is different in that MOSFETs are usedinstead of the TFTs forming the pixel portion 602 and the driver circuitportion 603.

Note that the structure of the present embodiment can be freely combinedwith any structures of Embodiments 1 to 4.

Embodiment 6

An EL display device formed by implementing the present invention is aself-light-emitting type, and has a superior visibility in a brightlocation in comparison with a liquid crystal display device, and alsohas a wide angle of view. Therefore it can be used as a display portionof various electronic equipment. For example, the self-light-emittingdevice of the present invention may be used in the display portion of a30 inch or larger (typically 40 inch or larger) diagonal EL display(display incorporating EL display device in the housing) forappreciation of a TV broadcast or the like by a large screen.

Note that all display devices for displaying information such as apersonal computer display, a display for receiving TV broadcasts, and adisplay for displaying advertisements, are included in EL displays.Further, the self-light-emitting device of the present invention canalso be used in the display portion of various other electronicequipment.

The following can be given as this type of electronic equipment of thepresent invention: a video camera; a digital camera; a goggle typedisplay (head mounted display); a navigation system; an audio playbackdevice (such as a car audio system or an audio component system); anotebook type personal computer; a game apparatus; a portableinformation terminal (such as a mobile computer, a cellular phone, aportable game machine, or an electronic book); and an image playbackdevice equipped with a recording medium (specifically, device preparedwith a display which plays back a recording medium such as a digitalvideo disk (DVD) and displays that image). In particular, a wide angleof view is important for a portable information terminal often seen froman oblique angle, and therefore it is preferable to use an EL display.Specific examples of those electronic devices are shown in FIGS. 15A to15F and FIGS. 16A and 16 ab.

FIG. 15A is an EL display, and includes a frame 2001, a support stand2002, and a display portion 2003, etc. The present invention can be usedin the display portion 2003. The EL display is a self-light-emittingtype, and therefore a back light is not necessary, and the displayportion can be made thinner than that of a liquid crystal displaydevice.

FIG. 15B is a video camera, and includes a main body 2101, a displayportion 2102, a sound input portion 2103, operation switches 2104, abattery 2105, an image receiving portion 2106, etc. The EL displaydevice of the present invention can be used in the display portion 2102.

FIG. 15C is a portion (right side) of a head mounted EL display, andincludes a main body 2201, a signal cable 2202, a head fixing band 2203,a display portion 2204, an optical system 2205, EL display device 2206,etc. The present invention can be used in the EL display portion 2206.

FIG. 15D is an image playback device equipped with a recording medium(specifically, a DVD playback device), and includes a main body 2301, arecording medium (such as a DVD) 2302, operation switches 2303, adisplay portion (a) 2304, and a display portion (b) 2305, etc. Thedisplay portion (a) 3334 is mainly used for displaying imageinformation, and the display portion (b) is mainly used for displayingcharacter information, and the EL display device of the presentinvention can be used in the display portion (a) and for the displayportion (b). Note that the image playback device equipped with therecording medium includes devices such as household game machines.

FIG. 15E is a portable (mobile) computer, and includes a main body 2401,a camera portion 2402, an image receiving portion 2403, operationswitches 2404, and a display portion 2405. The EL display device of thepresent invention can be used in the display portion 2405.

FIG. 15F is a personal computer, and includes a main body 2501, a frame2502, a display portion 2503, and a keyboard 2504. The EL display deviceof the present invention can be used in the display portion 2503.

Note that if the brightness of light emitted by EL materials increasesin the future, then it will become possible to use in a front type or arear type projector to expand and project light containing output imageinformation with a lens or the like.

Further, the above electronic devices often display informationdistributed through an electronic communication network such as theInternet and a CATV (cable television). In particular, there are moreand more opportunities that the electronic devices display dynamic imageinformation. Since the response speed of an EL material is very high, anEL display device is suitable for dynamic image display. However, ifoutlines between pixels are blurred, the whole dynamic image is blurred.Therefore, it is quite effective to use, as a display portion of anelectronic devices, the EL display device according to the presentinvention which clears outlines between pixels.

In addition, since the EL display device consumes power in the lightemitting portion, it is therefore preferable to use the EL displaydevice for displaying information so as to make the light emittingportions as few as possible. Consequently, when using the EL displaydevice in a display portion mainly for character information, such as ina portable information terminal, in particular a cellular phone or anaudio playback device, it is preferable to drive so as to form characterinformation by the light emitting portions while non-light emittingportions are set as background.

FIG. 16A is a cellular phone, and includes a main body 2601, a soundoutput portion 2602, a sound input portion 2603, a display portion 2604,operation switches 2605, and an antenna 2606. The EL display device ofthe present invention can be used in the display portion 2604. Note thatby displaying white color characters in a black color background, thedisplay portion 2604 can suppress the power consumption of the cellularphone.

FIG. 16B is an audio playback device, specifically a car audio system,and includes a main body 2701, a display portion 2702, and operationswitches 2703 and 2704. The EL display device of the present inventioncan be used in the display portion 2702. Further, a car audio system isshown in this embodiment, but the EL display device of the presentinvention can be used in a portable type or a household audio playbacksystem, too. Note that by displaying white color characters in a blackcolor background, the display portion 2704 can suppress the powerconsumption. This is especially effective in a portable type audioplayback device.

The applicable range of the present invention is thus extremely wide,and it is possible to apply the present invention to electric equipmentin all fields. Also, the electric equipment in this embodiment can alsobe realized by using any EL display device structured in Embodiments 1to 5.

Embodiment 7

In an EL element manufactured by using the present invention, it is alsopossible to use an EL material which can use phosphorescence fromtriplet excitation for light emission. A light-emitting device using anEL material, which can use phosphorescence for light emission candrastically improve the external light emission quantum efficiency. Thismakes it possible to lower the power consumption, prolong the life, andlighten the weight, of the EL element.

The following papers report that the external light emission quantumefficiency is improved using triplet exciton.

The structural formula of an EL material (coumarin pigment) reported byT. Tsutsui, C. Adachi, and S. Saito in Photochemical Processes inOrganized Molecular Systems, ed. K. Honda (Elsevier Sci. Pub., Tokyo,1991), p. 437 is as follows:

The structural formula of an EL material (Pt complex) reported by M. A.Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson,and S. R. Forrest in Nature 395 (1998), p. 151 is as follows:

The structural formula of an EL material (Ir complex) reported by M. A.Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, and S. R. Forrest inAppl. Phys. Lett., 75 (1999), p. 4, and by T. Tsutsui, M. J. Yang, M.Yahiro, K. Nakamura, T. Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, andS. Mayaguchi in Jpn. Appl. Phys., 38 (12B) (1999) L1502 is as follows:

If the above phosphorescence from triplet exciton can be used, inprinciple, external light emission quantum efficiency, which is three tofour times as much as that when fluorescence from singlet exciton isused, can be materialized.

Note that the structure of the present embodiment can be freely combinedwith any structures of Embodiments 1 to 6.

According to the present invention, failure film formation of anelectrode hole caused when a film of an organic EL material is formedcan be improved. Further, according to the present invention, since theelectrode hole can be filled up with a protective portion in variousmethods and in various shapes, film formation according to theconditions and the purpose can be performed, and failure light emissionof an EL layer due to short circuit between a cathode and an anode canbe prevented.

Although the present invention has been disclosed in conjunction withthe preferred embodiments of the invention, the present invention shouldnot be limited to the particular embodiments. For example, the presentinvention may be applied to an EL device having a different type ofswitching elements or a circuit for driving the EL elements.

1. A light-emitting display device comprising: a first and a secondswitching elements over a substrate; an interlayer insulating filmformed over the first switching element and the second switchingelement; a first pixel electrode and a second pixel electrode formedover the interlayer insulating film; a first insulator formed in a gapbetween the first pixel electrode and the second pixel electrode; alight-emitting layer formed over the first pixel electrode and the firstinsulator; and a third electrode formed over the light-emitting layerand overlapping the first pixel electrode, wherein the first pixelelectrode and the second pixel electrode are electrically connected tothe first switching element and the second switching element throughelectrode holes in the interlayer insulating film, respectively; andwherein a second insulator is formed in each of the electrode holes,from a same film as the first insulator.
 2. A light-emitting displaydevice according to claim 1, wherein the first insulator covers portionsof the first pixel electrode and of the second pixel electrode.
 3. Alight-emitting display device according to claim 1, wherein the firstinsulator and the second insulator comprise a material selected from thegroup consisting of acrylic resin, polyimide resin, polyamide resin. 4.A light-emitting display device according to claim 1, wherein the firstinsulator and the second insulator comprise a resin containing a highmolecular compound of siloxane.
 5. A light-emitting display devicecomprising: a plurality of switching elements over a substrate; aninterlayer insulating film over the switching elements; a plurality ofpixel electrodes over the interlayer insulating film; a light-emittinglayer over the plurality of pixel electrodes; and an electrode over thelight-emitting layer, wherein the plurality of pixel electrodes areconnected to the switching elements, respectively, wherein a firstinsulator is formed in at least one of spaces between the plurality ofpixel electrodes, and wherein at least one of the plurality of pixelelectrodes is connected to one of the switching elements through anelectrode hole in the interlayer insulating film, the electrode holebeing filled up with a second insulator.
 6. A light-emitting displaydevice according to claim 5, wherein the first and second insulatorscomprise a material selected from the group consisting of acrylic resin,polyimide resin, polyamide resin.
 7. A light-emitting display deviceaccording to claim 5, wherein the first and the second insulatorcomprise a resin containing a high molecular compound of siloxane.
 8. Alight-emitting display device comprising: a first and a second switchingelements over a substrate; an interlayer insulating film formed over thefirst and second switching elements; a first and a second pixelelectrodes formed over the interlayer insulating film; an insulatorformed in a gap between the first and the second pixel electrodes; alight-emitting layer formed over the first and the second pixelelectrodes and the insulator; and a third electrode formed over thelight-emitting layer opposed to the first and second pixel electrodes,wherein the first and second pixel electrodes are electrically connectedto the first and second switching elements, respectively; and wherein atop surface of the first pixel electrode and a top surface of theinsulator coincide with each other.
 9. A light-emitting display deviceaccording to claim 8, wherein the insulator comprises a materialselected from the group consisting of acrylic resin, polyimide resin,polyamide resin.
 10. A light-emitting display device according to claim9, wherein the insulator comprises a resin containing a high molecularcompound of siloxane.